The present invention, in some embodiments thereof, relates to monitoring and, more particularly, but not exclusively, to using EM radiation for monitoring changes of a cardiac performance.
Medical instruments in which an echo of a pulse of EM radiation is used to detect and locate structures in the human body are known, see YOUNG, J. D et. al. Examination of video pulse radar systems as potential biological exploratory tools in LARSEN, L. E., and JACOBI, J. H. (Eds.): ‘Medical applications of microwave imaging’ (IEEE Press, New York, 1986), pp. 82-105, which is incorporated herein by reference. Such medical instruments includes microwave imaging devices, which may be referred to as tissue sensing adaptive radar (TSAR) or imaging and other medical devices for detecting and possibly imaging internal biological tissues. The use of electromagnetic waves eliminates the need to expose the tissues to ionizing radiation, as performed during X-ray imaging, and to obtain relatively large tissue contrasts according to their water content.
During the last years, various methods and devices have been developed for diagnosing intrabody tissues of ambulatory patients using electromagnetic (EM) radiation. For example, International Patent Application Number IL2008/001198, filed on Sep. 4, 2008, which is incorporated herein by reference, describes a wearable monitoring device for monitoring at least one biological parameter of an internal tissue of an ambulatory user. The wearable monitoring device comprises at least one transducer configured for EM radiation to the internal tissue and intercepting reflections of the EM radiation therefrom in a plurality of continuous or intermittent EM radiation sessions during at least 24 hours, a processing unit configured for analyzing respective reflections and identifying a change in the at least one biological parameter accordingly, a reporting unit configured for generating a report according to the change, and a housing for containing the at least one transducer, the reporting unit, and the processing unit, the housing being configured for being disposed on the body of the ambulatory user.
Using EM radar for cardiac biomechanics assessment is mentioned in E. M. Staderini, “UWB radars in medicine,” IEEE Aerospace and Electronic Systems Magazine, vol. 17, no. 1, pp. 13-18, 2002, which the content thereof is incorporated herein by reference.
The most widespread system for the monitoring of the cardiac activity is the electrocardiograph (ECG). The information provided by ECG is related to heart electrical activity. With time, ECG data has become a useful tool in monitoring the health of an ambulatory patient's heart. A prominent type of ECG monitoring is Holter monitoring in which ECG data is acquired continuously over a 24 hour period. Data acquired by Holter monitoring is useful in identifying patients who are at risk of ventricular tachycadia. To date, it has been difficult to properly identify late potentials in the data acquired by Holter monitoring. Late potentials are low level electrical signals that cause late activation of the heart within its cycle. Such late potentials can cause premature contraction and, eventually, severe fibrillation. Such late potentials have been difficult to detect because they are of too low a level (i.e., approximately 5 microvolts) and too high a frequency (i.e., approximately 250 hertz) for detection by conventional Holter monitoring systems.